Polyaniline is an intrinsically conductive polymer (ICP) that has the potential to be used in a number of applications, such as LEDs, rechargeable batteries, EMI shielding, and smart windows. Another significant potential use is in the area of corrosion prevention. Corrosion is an estimated 200 billion dollar problem in the U.S. each year.
It has been found that polyaniline, can inhibit corrosion when applied to a metal surface. Conventional polyaniline, however, is limited by its processability (Gregory, Richard V., “Chapter 18: Solution Processing of Conductive Polymers: Fibers and Gels from Emerldine Base Polyaniline” in Handbook of Conducting Polymers, Eds. Skotheim, Terje A. et al., p. 437 (1998)). Emeraldine base, the nonprotonated, nonconducting form of polyaniline, has only limited solubility in organic solvents such as NMP, N,N-dimethylacetamide, and dimethylformamide. The doped conducting form, emeraldine salt, is insoluble in all common organic and polar solvents. The limited solubility of polyaniline makes it difficult to process and difficult to disperse evenly over a surface as a coating.
Lignosulfonic acid-doped polyaniline (hereinafter, ligno-pani; U.S. Pat. No. 5,968,417) is dispersible in water and fairly soluble in organic solvents such as dimethylsulfoxide (DMSO) and tetrahydrofuran (THF) in its conducting state due to the high solubility of the lignin (Viswanathan, T., U.S. Pat. No. 5,968,417; Sudhaker, M. et al., “Chapter 6: Conducting Waterborne Lignosulfonic Acid-Doped Polyaniline,” in Semiconducting Polymers, Eds. Hsieh, Bing R. et al., American Chemical Society, p. 76 (1999)). This provides increased processability as well as reduced cost for this polymer. It has been disclosed that ligno-pani can be used to coat fabrics (Viswanathan, U.S. Pat. Nos. 5,968,417 and 6,059,999).
There is currently a need for corrosion-preventing coatings. In particular, with increasing restrictions by the EPA on Volatile Organic Compounds (VOCs), chromate, and other heavy metal conversion coatings, alternative additives for corrosion inhibition which can be dispersed in water-based coatings are of increasing importance. Thus, preferred metal coatings would have the properties of being inexpensive, water-based, and avoid the use of volatile organic compounds and heavy metals.